High-frequency signaling system



Dec. 1-0, 1929. E F ARTE 1,739,351

HIGH FREQUENCY SIGNALING SYSTEM Filed Jan. 14, 1927 Inventor-z Emmett, F. Carter",

His Attorney.

I Patented Dec. 10, 1929 UNITED STATES.

PATENT oFFIcE EHMETT I. CARTER, OI SGHENECT ADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK HIGYLFREQUENGY SIGNALING SYSTEM Amman filed J'anuary 14, 1927. SerialNo. 161,188.

Myinvention relates to signaling systems and particularly to systems employing high frequency currents, and has for its purpose to provide a signaling system such that the 5 intensity of the receivedsignal will be automatically maintained at or below a predetermined level.

-It is well-known, that when the receiving circuits of a high frequency signaling sys impulses to control the power circuit to a transmission level. p

All of these systems have inherent disadtem have been adjusted for reception of signals from a distant station the signals from a near by station will be received in such great volume that they cannot be understood and may cause discomfort for the operator who is listening at the head phones. Likewise, it may result that during reception from a single station the transmission characteristics of the media over which the signals are being transmitted may vary causing the intensity of the received signals to fluctuate, thereby necessitating frequent readjustment of the receiving circuit to compensate for the variations in the transmission media andto maintain a desired volume level of the received signal. I Means have heretofore'be'en provided for" controlling the transmission level in high frequency systems. These means have usually involved relays whiclfioperate responsivel'y to the intensity of the received high frequency motor which affects appropriate adjustments in the transmission circuit. Others have involved relays which operate ,responsively to" the intensity of pilot frequencies transmitted over the same transmission media as the signal, while .still others have involved relays which operate responsively to changes in current passed through pilot wires which are sub jected to the same transmission conditions as the-media over which the desired signal is beingtransmitted. "Still other means have been provided for manually controlhng the vantages in that they. either require the presence of a skilled operator or are. complicated in their circuit construction necessitating the use of auxiliary carrier current generators, pilot wires and the like. Furthermore, the use of relays, motors and other instrumentalities having moving parts-intro-- delay in the op- 3 tuned portion of thesignaling circuit which impedance I propose to vary in response to the intensity oftheimpressed carrier currents to detune the tuned circuit and to shunt off a portion of the signal. For this impedance I prefer to employ an electron discharge device since the well-known characteristics of such devices are such that their impedance may be varied over a very wide range in response to a small variation in the electrical condition of the control element of the device.

The novel features which I believe to be.

characteristic of my invention are set forth with particularity in the appended claims.

My invention itself, however, both as to its organization and method of operation will best be understood by reference to the following description taken in connectionwith the accompanying drawings in which Fig. 1

illustrates diagrammatically one form of my invention; Fig. 2 illustrates my invention applied toa circuit including a grid bias detector; Fig. 3, illustrates my inventionapplied to a circuit including a gridleak detector,

and Fig. 4 shows shown in Fig. 2.

Referring ,firs 0 Fig. 1, 1 indicates an antenna, if the invention be applied to radio a modification of the circuit reception, or awire circuit if the invention be employed in carrier current reception. 3 'in dicates the coupling transformer for inductively connectlng the transmitting circuit and the receiving circuit with the antenna or the wire circuit. 4 indicates a detector tube which is associated with the receiving apparatus for the purpose of detecting the received'carrier signals and for transmitting them to the operators receivers or head phones Signalsare transmitted to this detector tube through a tuned link circuit 5,

which is inductively connected by means of a transformer 6, to the tuned input circuit 7 of the detector 4. For the purpose of-tuning the circuits 5 and 7 to resonate at the frequency of the signal which is to be received, condenser 8 in the link circuit 5 and a condenser 9 in the circuit 7 is provided. To one side of the tuned link circuit 5 is connected the anode 10 of the electron discharge device 11 through a suitable source of potential 12. With the other side of the tuned link circuit 5 is associated the cathode 13 of the electron discharge device through a circuit comprising. the conductor 14, resistance 15, part of battery 17, conductor 18, and conductor 19. With the one side of the circuit 7 is associated the anode ofthe electron discharge device 21 through a suitable source ofpotential 22. The cathode 23 of the electron discharge device 21, is connected to the opposite side of the tuned circuit 7 through "conductors 24, and the grid 31 .of the electron discharge device 21 is connected through the conductor to the cathode 13, of electron discharge device 11. A suitable by-passcondenser 27 is provided between the cathode 13 and the conductor 19 for the purpose of shunting the alternating currents out of the resistance 15 and the battery 17. A suitable source of potential 25 is provided for heating the cathodes of electron discharge device 21, and of thedetector 4. A similar source of potential 26 is provided for heating the cathode of the electron discharge device 11.

The operation of this form of my invention is as follows. During normal operation of the circuit when the volume of the received high frequency impulses is below a certain predetermined level and reception is taking place through the detector 4 in the usual way, the electron discharge device 11 will be inactive. This is because the source of potential 12, which is in series with that portion of the battery 17 which is between the contacts 28 and 29 through a circuit including the primary winding of the transformer 6, conductor 19, conductor 18, contact 28, battery 17, contact 29, resistance 15,

, conductor 14 and cathode 13, establishes a negative potential upon the anode 10 with respect to the cathode 13, such that no passage of electrons from the cathode to the anode and no' flow of current in this circuit can take place. The anode of'the electron discharge device 21 is similarly-biased by means of the battery 22 and the fbattery 17 through a circuit including the secondary winding of the transformer 6, but this bias is not so great but that a flow ofelectrons from the cathode 23 to the anode 20 will take place except when the grid 31 1s biased negatively with respect to the cathode 23. This bias is efiected by means of that portion of the battery 17 which is between the oathode connection 32 and the contact 29 through a circuit including the resistance 15, conductor 14, conductor 30 to the grid 31 Assuming that a change in the transmission characteristics of the media over which the signal is being transmitted has occurred, or that suddenly a nearby station for which the receiving clrcuit has not been adjusted -starts to transmit, or that for some other cause the intensity of the high frequency im pulses, which are impressed upon the receiving circuit increases a larger voltage will then be impressed upon the winding 33 of the coupling transformer 3. This voltage will overcome the negative potential of the anode .10 and a passage of electrons from the cathode 13 to the anode 10 will take place. Hence current will flow through the circuit including the cathode 13, conductor 14, re-

' sistance 15, contact 29, that portion of the battery 17, which is between the contact 29 and contact 28, contact 28, conductor 18, conductor 19, primary winding of the transformer 6, battery 12, anode 10 and thence through the space between the anode 10 and the cathode 13 back to the cathode. Thus a potential will be set up across resistance 15 which is opposed to and greater than that portion of the battery 17 which is between the cathode connection 32 and the contact 29 and the potential of the grid 31 will be correspondingly increased in the positive direction. The circuit through which this is effected has already been traced from the grid 31 through the conductor 30, conductor 14, resistance 15, contact 29, that portion of the battery which is between the contact 29 and the cathode connection 32, back to the cathode connectoin 32. This being the case current will flow from the anode 20 to the cathode 23through the conductors 24, bat-- tery 17 secondary winding of transformer 6, battery 22 back to the anode 20. The electron discharge device 21 will then constitute a comparatively low resistance shunt across the tuned circuit 7. The value of this resistance will dependupon the voltage across the resistance 15 which; in turn, varies with the received signal. This shunt will not only detune the circuit 7 but acting'through the 5 so that the resonance frequency of the circuit will .i-no longer be the frequency of the received signal.v This being the case, the efliciency of transmission of energy through the circuit will be greatly decreased and thevolume of the received signal at the vreceiver will be diminished. When this condition of high transformer-.6 it will detune the link circuit 4 intensity impulses has pla i device llor the resistance 15, and the rid 31' of the electron discharge device 21 wil again" assume its normal negative potential and the'shunt circuit through the electron discharge device 21 will no longer exist. Transmission through the circuit will again take place at the normal efficiency of the circuit. Hence, it appears Cthat the electron discharge device 11 operates as a relay for opening and closing the shunt circuit across the tuned circuit 7 responsively to the increase or decrease of volume of the impressed high frequency impulses.

In Fig. 2, I,have shown another and what I believe to be a better form of my invention,

in which I only employ one tube, in addi-' tion to those of the usual receiving circuit and cause this tube to operate responsively to the direct current flowing in the anode circuit of the detector 4. The circuits employed are substantially the same as those employed in Fig. 1, with the exception that the electron dischar e device 21 has been connected in shunt reIation to the tuned link circuit 5 and 'the source of direct current potential for controlling the electron discharge device 21 is derived from the anode circuit of the detector 4, rather than from the series circuit of an electron discharge device such as 11 in Fig. 1. In this figure I have shown a circuit including a grid bias detector.-

High frequency signals are impressed upon the grid of the detector by means of the condenser 34 connected in the input circuit 7.

The grid of the detector is supplied with a negative bias by means of the battery 17 through a resistance 35a The anode-of the detector 4 has a high positive direct current potential impressed by means of the battery 36 through the impedance 36. Impedance 36 may represent that of the receiver or.

that of the primary of an audio transformer leading to appropriate circuits which may be associated with the receiver. Connected in series with the circuit of the anode 4 is a resistance 15 which corresponds to the resistance 15 of Fig. 1. The grid 31 of the electron discharge device 21% is connected through a circuit including the resitance 38, negative biasbattery 39 and conductorv 40 to the negative side of the cathode 37 of detector 4. The cathode of the electron discharge device 21 is connected through a condoctor 41 to a point 42 in the anode circuit which is on the opposite side of the resistance 15 fromthe-cathode connection'43. With this connection'it is seen that the resistance 15 servesas a source of direct current potential for determining the bias upon. the

grid 31 of the electron discharge device 21'.

e electron discharge. rents aroundt to serve as a b -pass for the alternating-cure resistance 15'. The operationof this form of my invention is as follows: During normal operation of the circuit when the intensity of the received signals is below the predetermined value, the

pulses, then the direct current flowing in the plate circuit of'the detector will correspondingly increase causing an increase of direct current potential across the resistance 15'.

This potential is in series with but opposed to the grid bias battery 39 through a circuit as follows: cathode 23, conductor 41, cathode connection 42, resistance 15, cathode connection 43, conductor 40, grid bias battery 39, resistance 38 to the grid 31. Hence, upon an increase of potential across the resistance 15, thenegative bias upon the grid 31, due to the battery 39, will be overcome by the potential across the resistance 15 and the grid will assume a positive potential. Current will then flow from the anode 20 to the cathode'23, and the electron discharge device 21 will become a comparatively low resistance shunt across the primary of transformer 6, thereby detuning this transformer and its associated tuned circuits and greatly lessening the efiiciency of transmission through the circuit. This in turn will decrease the volume of received signal at the head phones.

In Fig. 3 I have shown another form of my invention as applied to a grid leak detector. It is well-known that in'detectors of this type direct currentgfiowing in the anode circuit which is connected to one side of the filament battery 25, just'as is. done in Fig. 2. Instead of providing a separate negative bias battery for the grid 31 of the electrondischarge device 21, this grid is connected through the conductor 40 directly to a low voltage tap on the anode battery 36. It is-to beunderstood, j

however, that a negative bias battery may be inserted in this circuit if desired. In this case the cathode 23 of the electron discharge device 21 is connected in parallel with the cathode 370i thedetector 4, thereby eliminating the necessity for an additional cathode battery.

In this case the anode circuit of a The operation of this form ofmyinvention ,4 across the resistance 15 having the polarity indicated in the drawing. 7 This polarity will be opposed to and greater than that of that portion of the battery 36 which is tapped off by the grid lead 40 and a negative potential will exist upon the grid 31 of the electron discharge device 21. Assuming that the amplitude of the impressed high frequency current increases for some cause, thereby causing the signal intensity .at the receiver to become greater than the predetermined value, then the direct current flowing in the anode circuit of the detector 4 will correspondingly diminish causing a drop in the. voltage across the resistance 15. This being true the potential of that portion of the battery 36, which is tapped off by the grid lead 40 will become effective upon the grid 31, and, cause the grid to assume a positive potential. Current will then fiow from the anode 20 to the cathode 23 and the electron discharge device 21 will become a comparatively low res stance shunt across the primary of the transformer 6, thereby detuning the transformer and its associated tuned'circuits. This being the case, the efficiency of transmission through the circuit will be greatly diminished and the volume of signal received at the head phones will be decreased.

In Fig. 4 I have shown a modification of that form of my invention which is shown in Fig. 2. The circuit is the same as that shown inFig. 2'with the exception that the control electron discharge device 21 has been connected across the tuned circuit 7 and the tuned link circuit 5 has been omitted. I have further modified the circuit by tapping the grid lead 40 to the negative bias battery 17, 1

thereby eliminating the necessity for a grid bias battery 39. In all other respects the circuit is,,the same. The operation of this formof my invention will be understood I from the operation of Fig. 2.

It may thus be seen that I have .p rovided a volume control device which is y simple in its circuit structure and in and which does not. require the attention of a skilled operator; and which operates Idirectly in response to the received high frequency wave upon which the signal is impressed. My invention has the further advantage that it is completely electrical in its operation and does not involve any mechanical moving parts, such as motors, relays, and the like-, which introduce undesirable effects into the operation of the system. Hence, my device is practically instantaneous in its operation. My invention has the further ad vantage; that it involves the addition of\a single vacuum tube to the usual detector circuits and that it may be applied with facilityand without great expense to any circuit where the usual detector and its associated tuned circuits are employed.

While I have shown and described my invention with particular reference to receiving circuits it will be apparent that it is not so limited and that it may be applied to transmittingcircuits as well. Itwill also be apparent that my invention is not limited to the particular embodiment shown but that many modifications in the circuit arrangements and instrumentalities employed in carrying out my invention may be made without departing from the scope thereof as set forth in the appended claims.

' What I claim as new and desire to secure by Letters Patent of the United States, is:

' 1. In a receiving circuit employing a detector, a volume control device, comprising an electron discharge device having a cathode and an anode, said cathode being connected to one side of said receiving circuit and said anode being connected to the other side of said receiving circuit to form a shunt, and

electrical means responsive to the direct current flowing in said detector for controlling the impedance between said cathode and said anode.

2. In a receiving circuit employing a detector. a volume control device, comprising an electron discharge device having a cathode, an anode and a grid, said cathode being connected to one side of said receiving circuit and said anode being connected to the other side of said receiving circuit to form a shunt, and electrical means responsive to the direct current flowing in said detector for varying the potential on said grid.

3. In a high frequency signaling system comprising a plurality of tuned circuits coupled to each other, a volume control device comprising an electron discharge device having an anode and a cathode, said anode being connected to one side of one of said tuned circuits, said cathode being connected to the other side of said tuned circuit and means a ociated with another one of said circuits f varying the resistance between said Ride and said anode responsively to the intensity of the impressed high frequency impulses.

4. In a high frequency signaling system pled to each other, a volume control device comprising a plurality of tuned circuits coucomprising an electron discharge device,.

of said tuned circuits for varying the 'potential on said grid responsively to the intensity of the lmpressed high frequency impulses. v

5. In a h gh frequency signaling system pled to each other, a'volume control device comprising an electron discharge device having an anode, a cathode and a grid, said anode'being connected to one side of one of said tuned circuits and said cathode being connected to the other side of said tuned circuit and means res onsive to the intensity of. the impressed hig frequency impulses forr controllingthe potential of said grid.

6. In a signaling system comprising a plurality of tuned'circuits coupled to each other, a volume control device comprising an electron discharge device associated with one of .said tuned circuits having an anode, a cathode and a grid, said anode being connect-, ed to one side of said tuned circuit and said cathode being connected to the other side of said tuned circuit, a second electron dis charge device associated with another one of said tuned circuits,and a resistor connected in series with the anode circuit of said second electron discharge device one side of said resistor being connected to the cathode of said first electron discharge device and the other side of said resistor being connected to the grid of said first electron discharge device. a 7. In a signaling system comprising a tuned so circuit, a volume control device comprising an electron discharge device'associated with said tuned circuit and having an anode, a cathode and a grid, said anode being connected to one side of said tune circuit and said cathode being connected tothe other side of said tuned circuit, to form a shunt, a second electron discharge device associated with said tuned circuit, a resistor in series with the anode circuit of said second electron discharge device and means for varying the potential on the grid of said first discharge I device in response to the potential on said resistance. Y

8. In a signaling system consisting ofa plurality of tuned circuits coupled to each other, a volume control device comprism a vacuum tube connected in shunt relation with one of said tuned circuits, a second vacuum tube having its input circuit associated with another of said tuned circuits, and a resistance in series with the output circuit of said \second vacuum tube for controlling-theimpedance of said first vacuum tube and thereby detuning said' tuned circuits.

In a signaling system consisting of a plurality of tuned circuits coupled to each other, avolume control 'devicecomprising a vacuum tube connected in shunt relation with one of-said tuned circuits, a second vacuum i 10. In a signaling system including a plu-. I

tube having its input circuit associated with rality of associated tuned circuits, a volume control device comprising a normally inactive shunt associated with one of said tuned cir cuits and means associated with another one of said tuned circuitsto yary the impedance of said shunt and detune said tuned circuit.-

11. In a high frequency receiving circuit including a plurality of associated tuned circuits, a volume control device comprising a normally inactive shuiftassociatedwith one of said tuned circuits and means associated tube associated with one of said tuned cir-' cuits having a cathode, an anode and a grid, said cathode and said anode being connected in circuitrelation across said tuned circuit, a detector associated with another of said tuned circuits and having an output circuit, a resistance in series withsaid output circuit, one side of said resistance being maintained at the potential of said cathode and the other side of said resistance being associated with said grid.

13. In a receiving circuit, a volume control device comprising a plurality of associated tuned circuits, a normally inactive shunt for one of said tuned circuits, a detector in said receiving circuit and means associated with the output circuits of said detector for ren dering said shunt active.

' 14. In a receiving circuit, a volume control device comprising a plurality of associated tuned circuits, a vacuum tube having an anode, a cathode and a grid, the circuit of said anode and said cathode being connected in shunt relation with one of said tuned circuits, a detector in said receiving circuit having an output circuit, a resistance in series with said output circuit, one terminal'of said resistance being connected to said cathode electrical means responsive to the direct current flowing in said detector for controllin the tuning of said timed circuit thereby to a feet the signal output from said detector.

16. In a high frequency receiving circuit, a

detector, 'a tuned circuit for controlling the input to said detector and means responsive to current flowingin said detector for detuning said tuned circuit in accordance with the gradations in intensity of said'current over a range'of variations thereof.

17. In a high frequency receiving circuit,

a detector, a tuned circuit for controlling the input to said detector, a shunt for detuning said tuned circuit, and means responsive to the received high frequency impulses for controlling said shunt in accordance with the gradations in intensity of said current over a range of variations thereof.

18. In a high frequency receiving circuit, a detector, means connected in shunt to said 10 receiving circuit for detuning the receiving circuit to control the input to said detector and electrical means responsive to said de-v tector for controlling said first means.

19. In combination, a high frequenc receiving circuit, means including a tuned circuit for controlling the intensity of the out- I put currents from said receiving circuit and means responsive tothe intensity of the received high frequency currents for detuning 00 said tuned circuit in accordance with the gradations in intensity of said currents over a range of variations thereof, said means-including an electron discharge device connected in shunt with said tuned circuit.

In witness whereof, I have hereunto set my hand this 13th day of January, 1927.

Ell/IM'E'IT F. CARTER; 

